EP3092672A1

EP3092672A1 - Flow-guiding plate for a fuel cell

Info

Publication number: EP3092672A1
Application number: EP15702522.2A
Authority: EP
Inventors: Jean-Philippe Poirot-Crouvezier
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2014-01-07
Filing date: 2015-01-06
Publication date: 2016-11-16
Anticipated expiration: 2035-01-06
Also published as: FR3016243A1; US20190097246A1; JP6556733B2; US10170774B2; EP3092672B1; US10680255B2; US20160336604A1; FR3016243B1; JP2017502473A; WO2015104492A1

Abstract

The invention relates to a flow-guiding plate (53) for a fuel cell, including a conductive sheet comprising a relief: defining alternating flow channels on first and second faces (55), two successive channels (553, 554) on the first face (55) being separated by walls (559); defining first and second access holes at the ends of each of the flow channels on the second face and of a first group of flow channels (553) on the first face; defining a flow restriction (555, 556) in each flow channel of a second group of flow channels on the first face (55), the cross-section of the flow restrictions being smaller than the cross-section of the access holes to the flow channels of the first group, the first face (55) comprising alternating flow channels of the first group (553) and alternating flow channels of the second group (554).

Description

FLOW GUIDE PLATE FOR BATTERY A

COMBUSTIBLE

The invention relates to fuel cells, and in particular fuel cells comprising an alternation of proton exchange membranes and bipolar plates.

Fuel cells are envisaged as a power supply system for large scale motor vehicles in the future, as well as for a large number of applications. A fuel cell is an electrochemical device that converts chemical energy directly into electrical energy. A fuel such as dihydrogen or methanol is used as the fuel of the fuel cell.

In the case of dihydrogen, it is oxidized and ionized on one electrode of the cell and an oxidizer is reduced on another electrode in the cell. The chemical reaction produces water at the cathode, with oxygen being reduced and reacting with the protons. The great advantage of the fuel cell is that it avoids releases of atmospheric pollutants at the place of generation.

Proton exchange membrane fuel cells, called PEMs, operate at low temperatures and have particularly advantageous compactness properties. Each cell comprises an electrolyte membrane allowing only the passage of protons and not the passage of electrons. The membrane comprises an anode on a first face and a cathode on a second face to form a membrane / electrode assembly called AME.

At the anode, dihydrogen is ionized to produce protons crossing the membrane. The electrons produced by this reaction migrate to a flow plate and then pass through an electrical circuit external to the cell to form an electric current. At the cathode, oxygen is reduced and reacts with the protons to form water.

The fuel cell may comprise several so-called bipolar plates, for example made of metal, stacked on top of one another. The membrane is disposed between two bipolar plates. Bipolar plates may include channels and outlets for guiding reagents and products to / from the membrane, guiding coolant, and separating different compartments. Bipolar plates are also electrically conductive to form collectors of electrons generated at the anode. Bipolar plates also have a mechanical function of transmission of clamping forces of the stack, necessary to the quality of the electrical contact. Gaseous diffusion layers are interposed between the electrodes and the bipolar plates and are in contact with the bipolar plates.

Electronic conduction is performed through the bipolar plates, ionic conduction being obtained through the membrane.

The bipolar plates continuously feed the reactive surfaces of the electrodes into reagents, as and when they are consumed. The distribution of the reagents to the electrodes should be as homogeneous as possible over their entire surface. The bipolar plates comprise networks of flow channels ensuring the distribution of reagents. A network of flow channels is dedicated to the anode fluid, and a network of flow channels is dedicated to the cathodic fluid. The networks of anode and cathode flow channels are never in communication inside the cell, in order to avoid the direct combustion of the fuel and the oxidant. Reaction products and non-reactive species are flow-stripped to the outlet of the distribution channel networks. In most architectures encountered, the bipolar plates have flow channels through which cooling fluid flows, allowing the evacuation of the heat generated.

There are mainly three modes of circulation of the reagents in the flow channels:

the serpentine channels: one or more channels traverse the entire active surface in several round trips.

the parallel channels: a bundle of parallel and through channels runs through the active surface from one side to the other.

the interdigital channels: a bundle of parallel and clogged channels runs through the active surface from one side to the other. Each channel is clogged either on the inlet side or the fluid outlet side. The fluid entering a channel is then forced to pass locally through the gas diffusion layer to join an adjacent channel and then reach the fluid outlet of this adjacent channel.

The flow channels may be rectilinear or slightly wavy.

The most commonly used materials for bipolar plates are the carbon-polymer composite and the stamped metal.

The stamped metal proves to be a solution favoring the lightening and the compactness of the piles. The bipolar plates then use thin metal sheets, for example stainless steel. The flow channels are obtained by stamping. Most frequently, a first flow plate is used in the form of a first stamped sheet defining the anode flow channel and a second flow plate in the form of a second pressed sheet defining the cathodic flow channel. These two plates of the flow plates are joined back to back by welding to form a bipolar plate. A cooling fluid flow channel is provided in the space between the sheets.

The carbon-polymer composite technology allows for greater flexibility in designing flow channels by molding thicker plates.

FR2973583 proposes to remove the coolant channel in a bipolar plate out of two. With bipolar sheet metal plates, the bipolar plate devoid of coolant channel includes a single stamped sheet, which lighten the fuel cell. The cathodic flow channels are formed on a first face of the sheet, while the anodic flow channels are formed on the other face of the sheet.

The design of these channels is then closely related, since the anodic face is the negative of the cathodic face. Nevertheless, the design of the channels must ensure that the flows in the single-sheet bipolar plates are similar to those in the two-plate bipolar plates, so as not to create a power imbalance between the different cells. Moreover, it is desirable for the same sheet to be used interchangeably for a single sheet bipolar plate or to form a bipolar plate with two plates.

An additional design constraint relates to the pressure losses in the flows of reagents, these pressure drops must have the same order of magnitude at the anode and at the cathode. This constraint affects the respective sections of the fuel flow and oxidizer channels. This constraint complicates the design of a bipolar plate to a single sheet.

For dihydrogen used as fuel, the passage section in the anode channels must be lower than that in the cathode channels in order to obtain a pressure drop of the same order of magnitude. Indeed, the hydrogen is less viscous than the oxidant circulating at the cathode and its flow is lower.

The molar flow rate of dihydrogen consumed in a cell is equal to I /, I being the electric current produced and F the Faraday constant. The molar flow of air consumed is equal to 1 .2 * I / F.

In practice, the fuel and oxidant rates introduced into the cells are always greater than the flow rates consumed, according to a factor of increase. For dihydrogen, the mark-up factor is generally between 1 and 2.5. For air, the increase factor is generally between 1.2 and 3, to ensure a sufficient amount of oxygen output. Thus, for a given current I, the ratio between the molar flow rates of air and of hydrogen is at least 2, and most commonly between 3 and 5.

The viscosity of the wet dihydrogen is of the order of 8 * ^10-6 to 1 3 * 1 0 ⁶

Pa.s, depending on the temperature and the moisture content. The viscosity of moist air is of the order of 1 2 * 1 0 ^"6 to 21 * 1 0 ^{" 6} Pa.s.

When the flow channels of a bipolar plate are identical on the hydrogen and air side, a ratio is obtained between the pressure losses for air and for the dihydrogen between 2 and 1 0. To balance the pressure losses, it is It is desirable to reduce the flow section of the hydrogen flow channels with a ratio between 2 and 10 relative to the passage section of the air flow channels.

Several alternatives are known to reduce this disproportion of pressure drops, with associated disadvantages:

to increase the width of the cathodic flow channels by producing anode channels having the finest width that is industrially possible to produce. This is in contradiction with the search for the optimum efficiency of electronic conduction in the fuel cell, which is generally achieved by reducing as much as possible the width of the flow channels;

realize less flow channels at the anode than at the cathode. The distance between two anode channels increases, as does the width of the teeth separating the channels. This structure is unsuitable for a single-plate bipolar plate because the electronic conduction from the cathodes is then strongly affected;

-to reduce the depth of the anodic flow channels. This structure is unsuitable for a single-plate bipolar plate because the anode and cathode channels automatically have the same depth and are therefore affected by this decrease in depth.

The invention aims to solve one or more of these disadvantages. The invention aims in particular to allow the use of the same sheets for a bipolar plate with a single flow plate and for a bipolar plate with double flow plates, without anodic and cathodic flow disparities for these two types of bipolar plates. , and promoting a homogenization of the charge losses between the anode channels and the cathode channels. The invention thus relates to a fuel cell flow guide plate as defined in the appended claims. The invention further relates to a fuel cell as defined in the appended claims.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

FIG 1 is an exploded perspective view of an example of a fuel cell;

FIG. 2 is a perspective view of flow channels on a first face of a first embodiment of a metal sheet for a fuel cell flow plate;

FIG. 3 is a view from above of the first face of the metal sheet of FIG. 2;

FIG. 4 is a cross-sectional view of the metal sheet of FIG. 2 at access ports to flow channels;

FIG 5 is a cross-sectional view of the metal sheet of Figure 2 in its middle part;

FIG. 6 is a cross-sectional view of the metal sheet of FIG. 2 at a second end of the flow channels;

FIGS. 7 and 8 are perspective views of the second face of the sheet of FIG. 2, at the access orifices to the flow channels;

FIG 9 is a cross-sectional view of a fuel cell including different bipolar plates formed from metal sheets of Figure 2;

FIGS. 10 to 13 illustrate different longitudinal sectional views of the fuel cell of FIG. 9;

FIGS. 14 and 15 are perspective views of the first face of second and third embodiments of metal sheets;

FIG. 16 is a cross-sectional view of a variant of the first embodiment of a metal sheet at access orifices to the flow channels.

Figure 1 is a schematic exploded perspective view of a stack of cells 1 of a fuel cell 4. The fuel cell 4 comprises a plurality of cells 1 superimposed. The cells 1 are of the proton exchange membrane or polymer electrolyte membrane type.

The fuel cell 4 comprises a fuel source 40. The fuel source 40 supplies an inlet of each cell 1 with dihydrogen. The fuel cell 4 also comprises a source of oxidant 42. The source of oxidant 42 supplies an inlet of each cell 1 with air, the oxygen of the air being used as an oxidizer. Each cell 1 also includes exhaust channels. Each cell 1 also has a cooling circuit.

Each cell 1 comprises a membrane / electrode assembly 1 1 0 or

AME 1 1 0. A membrane / electrode assembly 1 1 0 comprises an electrolyte 1 13, a cathode 1 1 2 (not shown in Figure 1) and an anode 1 1 1 placed on either side of the electrolyte and fixed on this electrolyte 1 1 3.

Between each pair of adjacent MEAs, a bipolar plate is disposed. The fuel cell 4 here comprises alternating bipolar plates 51 and 52.

The bipolar plates 51 include a flow plate formed of a single metal sheet or foil 53. In a bipolar plate 51, the relief of a first face of its metal sheet defines the anodic flow channels, and the relief of a second face of its metal sheet defines the cathodic flow channels.

Bipolar plates 52 include two flow plates 53. Each of these flow plates 53 includes a metal sheet or sheet. The sheets are superimposed and fixed together by means of welds 54. In a bipolar plate 52, the relief of a face of a first flow plate 53 defines the anodic flow channels and the relief of a face a flow plate 53 defines the cathodic flow channels. A coolant flow channel is provided between the metal plates of the flow plates 53 of a bipolar plate 52.

The metal sheets forming the flow plates 53 of a bipolar plate 52 are identical. The metal sheets forming the flow plates 53 of the bipolar plates 51 and 52 are identical. Thus, the same design and the same manufacturing method can be used for the manufacture of the metal plates of the flow plates 53 of the bipolar plates 51 and 52. The metal sheets are for example formed of stainless steel, of alloy steel, of titanium alloy, aluminum alloy, nickel alloy or tantalum alloy.

In a manner known per se, during the operation of cell 1:

dihydrogen flows in an anode flow conduit between a bipolar plate and a 1 1 1 anode;

air flows in a cathodic flow conduit between a bipolar plate and a cathode January 1. At the level of the anode 11, the dihydrogen is ionized to produce protons that pass through ΑΜΕ 1 1 0. The electrons produced by this reaction are collected by the bipolar plate disposed opposite this anode 1 1 1. The electrons produced are then applied to an electrical charge connected to the fuel cell 4 to form an electric current. At the cathode 1 1 2, oxygen is reduced and reacts with the protons to form water. The reactions at the anode and the cathode are governed as follows:

¾ → 2H + 2e at the level of the anode;

4.H + 4e + 0-2 → 2¾Q at the cathode.

During its operation, a cell of the fuel cell usually generates a DC voltage between its anode and its cathode of the order of 1 V. The catalyst material used at the anode 11 1 advantageously includes platinum, for its excellent performance. catalyst.

Figure 2 is a perspective view of anodic side flow channels of a first embodiment of a conductive sheet of a flow guide plate 53 according to the invention. Figure 3 is a top view of the plate 53. Such a flow guide plate 53 can be used to form different types of bipolar plates, as detailed below.

The plate 53 has a first face 55 illustrated in FIG. 2 and a second face 56. The relief of the flow guide plate 53 defines an alternation of flow channels on the opposite faces 55 and 56. Thus, two channels successive flow of the same face of the plate 53 are separated by walls 559 delimiting a flow channel of the other face. The flow channels of the faces 55 and 56 extend in the same longitudinal direction. In this example, the flow channels are substantially straight.

At the face 55, the flow channels are split into first and second groups.

Access ports 551 open into flow channels 553 of the first group. The access ports 551 are disposed at a first end of the flow channels 553. A first flat portion 535 forms a flow guide surface extending between the various access ports 551. An inclined wall 557 forms a junction between an access orifice

551 and the middle part of its flow channel 553.

At the second end of the flow channels 553, access ports 552 open into the flow channels 553 of the first group. A second flat portion 536 forms a flow guiding surface extending between the various access ports 552. An inclined wall 558 forms a junction between the access ports 552 and the middle portion of their flow channel 553. .

The cross section of each flow channel 553 in its middle portion, between its access ports 551 and 552, is greater than the cross section at the access ports 551 and 552. The inclined walls 557 and 558 are thus extend in depth to a flat bottom of the flow channel 553. The middle portion of the flow channels 553 is thus devoid of flow restriction.

To ensure homogeneous pressure drops in the different flow channels 553, they have the same cross section in their middle part.

The face 55 has flow channels 554 of the second group. The face 55 comprises an alternation of flow channels 553 and 554 in a transverse direction. In the embodiment illustrated in Figure 2, the flow channels 554 have a wall 556 at their first end and a wall 555 at their second end. Each wall 555 extends from the bottom of a flow channel 554 to the top of the flat portion 536. Each wall 556 extends from the bottom of a flow channel 554 to the top of the Thus, the cross section of the flow channels 554 at the walls 555 and 556 is smaller than the cross section of the access ports 551 and 552 to the flow channels of the first group. Each of these walls 555 and 556 thus forms a flow restriction of a flow channel 554. Each flow channel 554 thus has at least one flow restriction. The passage section of a flow restriction is defined as the cross section of the flow channel at this flow restriction. The walls 555 and 556 extend here to the top of their flow channel 554 and to the bottom of the flow channels 563 of the face 56 detailed thereafter.

The relief of the flow guide plate 53 delimits flow channels 563 at the face 56. FIGS. 7 and 8 illustrate in perspective the first ends of two types of access orifices 561 to the channels 56. flow 563. Each flow channel 563 is delimited with respect to the flow channels 553 and 554 of the face 55 through walls 559. The flow channels 553 and 554 comprise respective bottoms 565 and 566 intended to form, for example, cathodic conduction contacts at the face 56.

As illustrated in these figures, the alternation of the flow channels 553 and 554 on the face 55 results in two types of flow channels 563 on the face 56. The cross section of each flow channel 563 in its middle portion , between the access ports at its longitudinal ends, is greater than the cross section at these access ports. Inclined walls thus extend in depth from an access port to a flat bottom of their flow channel 563. The middle portion of the flow channels 563 is thus devoid of flow restriction.

It can be seen that, due to the alternation of the flow channels 553 and 554, the two types of flow channels 563 and their access orifices are symmetrical to one another with respect to a longitudinal plane. perpendicular to the average plane of the plate 53. Therefore, the pressure drops across the two types of flow channels 563 will be exactly the same. To ensure homogeneous pressure drops in the different flow channels 563, they have the same cross section in their middle part.

In this embodiment, two successive flow channels 563 are in communication at each of their ends, because of the passages formed to arrange the walls 555 and 556 at the access ports. Consequently, any dispersions of pressure drops between two successive channels 563 can be homogenized by such a communication.

Fig. 4 is a cross-sectional view of the plate 53 in the flat portion 535. Fig. 5 is a cross-sectional view of the plate 53 in the middle portion of the flow channels. Figure 6 is a cross-sectional view of the plate 53 at the access ports 552.

The flat portion 535 extends between the access ports of the first end of the flow channels 563. The flat portion 535 thus forms a tundish between the flow channel access ports 563 at that first end. .

The flat portion 536 extends between the access ports of the second end of the flow channels 563. The flat portion 536 thus forms a splitter between the flow channel access ports 563 at this second end. .

The walls 559 provide a separation between the flow channels of the two faces. The bottom of a channel 563 is thus disposed at the top a channel 553 or 554, and vice versa. The bottoms of the various flow channels are intended to form conductive surfaces for collecting the electric current to pass through the guide plates 53.

The access ports to the flow channels 563 have the same section at both ends of these flow channels. The access orifices 562 of the second end of the flow channels 563 are illustrated in FIG. 6. These access orifices 562 here have a height corresponding to half the height of the channels 563. The assembly of two plates guide 53 in a stack of fuel cell cells 4 is thus facilitated.

The plate 53 is here formed of a metal sheet pressed to give it a relief. The shape of the face 55 is therefore the complementary or the negative of the shape of the face 56. The plate 53 may for example be made by stamping a metal sheet.

In this example, the flow channels 553 and 554 have the same cross section over at least 75% of their median portion. Thus, the bottom of the flow channels 554 provides a very large area for collecting cathodic current as appropriate.

In this example, the flow channels 553, 554 and 563 have an identical cross section in their middle part. Consequently, these channels may have the minimum width corresponding to their formation technology, and this in order to optimize the homogeneity of distribution of the current through the bipolar plate to be formed. Furthermore, the use of the same cross sections for the two-sided flow channels facilitates the assembly of two flow guiding plates 53 to form a bipolar plate.

In this example, the flat portions 535 and 536 are placed at the same height and the flow channels 553, 554 and 563 have the same depth with respect to these flat portions 535 and 536.

In the example, the access ports 551 are intended to communicate with an opening 40 formed through the flat portion 535. The access orifices at the first end of the flow channels 563 are intended to communicate with an opening 43 formed through the flat portion 535. The openings 40 and 43 are intended to be isolated from each other by means of joints, in a manner known per se. The access ports 552 are intended to communicate with an opening 41 formed through the flat portion 536. The access orifices 562 at the second end of the channels 563 are intended to communicate with an opening 42 formed through the flat portion 536. The openings 41 and 42 are intended to be isolated from each other by means of joints, in a manner known per se. Fig. 9 is a cross-sectional view of an example of a fuel cell 4 using flow guide plates 53 as detailed above.

The fuel cell 4 comprises membrane / electrode assemblies 1 1, 12 and 13. Each membrane / electrode assembly here comprises a gas diffusion layer 21 placed in contact with an anode 11 1. The anode 11 1 is fixed on a proton exchange membrane 1 13. A cathode 12 is fixed on the proton exchange membrane 1 13. A gaseous diffusion layer 22 is placed in contact with the cathode 1 12.

The fuel cell 4 further comprises flow guide plates 531, 532 and 533 as detailed with reference to FIGS. 1 to 8. The flow guide plate 531 here in itself forms a bipolar plate 51 disposed between the membrane / electrode assembly 11 and the membrane / electrode assembly 12.

The bottom wall of the flow channels 563 is here in contact with the gas diffusion layer 21 of the membrane / electrode assembly 12. The bottom wall of the flow channels 553 and 554 is here in contact with the gas diffusion 22 of the membrane / electrode assembly 1 1.

The flow guide plates 532 and 533 here form a bipolar plate 52 disposed between the membrane / electrode assembly 12 and the membrane / electrode assembly 13. The bottom wall of the flow channels 563 of the plate 532 is here placed in contact with the bottom wall 566 of the flow channels 554 of the plate 533. The plate 532 can be fixed to the plate 533 by means of welds (not illustrated) promoting electrical conduction between the plates 532 and 533 .

Flow circuits 57 are thus formed between the plates 532 and 533 by the association:

flow channels 554 of the plate 532 with flow channels 563 of the plate 533;

flow channels 553 of the plate 532 with flow channels 563 of the plate 533.

The bottom wall of the flow channels 554 of the plate 532 is here in contact with the gas diffusion layer 22 of the membrane / electrode assembly 12. The bottom wall of the flow channels 563 of the plate 533 is here in contact with the gas diffusion layer 21 of the membrane / electrode assembly 13.

It can be seen that the use of plates 531 to 533 having the same geometry makes it possible to form two different types of bipolar plates 51 and 52, while guaranteeing:

identical identical fuel flow rates through these bipolar plates;

the same respective oxidant flow rates through these bipolar plates.

The geometry of an object is usually defined by the shape of an object or its morphological characteristics.

The flow channels 563 of the plate 531 are intended to be traversed by oxidant, for example air. The flow channels 553 of the plate 531 are intended to be traversed by fuel, for example dihydrogen. The flow channels 554 are not intended to be traversed by a flow (or marginally by flow through the diffusion layers) due to the presence of flow restrictions, despite the same cross-sectional area. flow channels 553 and 554 over most of their middle part. For the same flow conditions, the pressure drop across the flow channels of the face 55 is greater than the pressure drop across the flow channels of the face 56.

Thus, it is possible to homogenize the pressure losses in the fuel and oxidant flows, despite differences in molar flow rates and differences in viscosity of the fluids in these flow channels. Furthermore, the presence of the walls 555 and 556 does not alter the homogeneity of the fluid distribution at the face 56.

The flow channels 563 of the plate 532 are intended to be traversed by oxidant. The flow channels 553 of the plate 533 are intended to be traversed by fuel. As in the previous case, the flow channels 554 of the plate 533 are not intended to be traversed by fuel, due to the presence of flow restrictions.

The pressure losses for the fuel are therefore identical for the two types of bipolar plates 51 and 52. The pressure drops for the oxidant are also identical for the two types of bipolar plates. In the oxidizer flow channels, the flow of gas is between an inlet and an outlet of the same flow channel 563. The flow is here of the parallel type.

In the fuel flow channels, the flow of gas takes place between an inlet and an outlet of the same flow channel 553. The flow is here of the parallel type.

The bipolar plate formed of the plates 532 and 533 comprises a flow circuit 57 intended to be traversed by coolant. In order to lighten the bipolar plate formed of the plate 531, it is devoid of coolant flow circuit.

Figures 10 to 13 are longitudinal sectional views for illustrating different flow of fluids through the bipolar plates 51 and 52. The dashed flows correspond to flows of coolant. Discontinuous flows correspond to fuel flows. Solid flows correspond to flows of oxidizer. In order to allow the formation of bipolar plates 51 with single plate 53 and bipolar plates 52 with double plates 53, in order to be able to use the same plate geometry 53, these advantageously have an axis of symmetry. The axis of symmetry is typically perpendicular to a median plane of the plate.

Fig. 14 is a perspective view of anodic side flow channels of a second embodiment of a conductive sheet of a flow guide plate 53 according to the invention. This second embodiment is distinguished from the first embodiment by the presence of additional flow restrictions in the flow channels 554. Additional walls 555 are thus arranged to close the middle portion of the flow channels 554.

In this embodiment, two successive flow channels 563 are thus in communication at their median parts, because of the passages formed to arrange the walls 555 and 556. Therefore, any pressure drop dispersions between two successive channels 563 can be further homogenized by such communication. Fig. 15 is a perspective view of anodic side flow channels of a third embodiment of a conductive sheet of a flow guide plate 53 according to the invention. This third embodiment is distinguished from the second embodiment by the absence of flow restrictions at the ends of the flow channels 554. Flow restrictions are here provided in the middle portion of the flow channels 554. Additional walls 555 are thus arranged to close off the median portion of the flow channels 554.

In this embodiment, two successive flow channels 563 are thus in communication at their median parts, because of the passages formed to arrange the walls 555 and 556. Therefore, any pressure drop dispersions between two successive channels 563 are still homogenized by such communication. FIG. 16 is a sectional view of a variant of a flow plate

53 at a first end of the flow channels. The flow plate 53 differs from that of the variant of FIGS. 1 to 8 by the geometry of the walls 555 and 556. The walls 555 and 556 do not extend to the top of their flow channel 554 (or not extend to the bottom of the 563 flow channels interposed). Therefore, a flow can pass through a flow channel 554 by surmounting the walls 555 and 556, but with pressure drops much greater than the pressure losses through a flow channel 553. Advantageously, the walls 555 and 556 are extend at least up to three-quarters of the depth of the flow channels 563 of the face 56.

In the illustrated examples, the flow channels have a rectilinear shape in the longitudinal direction. Of course, other geometries of flow channels may be provided, for example flow channels having corrugations along their longitudinal direction.

Claims

1. Flow control plate (53) for a fuel cell, characterized in that it includes a conductive sheet having a relief:

defining an alternation of flow channels on opposite first and second faces (55, 56) of the sheet, two successive flow channels (553, 554) of the first face (55) being separated by walls (559); ) delimiting a flow channel (563) of the second face (56), said flow channels of the first and second faces extending in the same longitudinal direction;

defining first and second access orifices respectively at the first and second ends of each of the flow channels (563) of the second face (56) and a first group of flow channels (553) of the first face, the cross section of each of these flow channels between its first and second ends being greater than the cross section of its first and second access ports;

defining a flow restriction (555, 556) in each flow channel of a second group of flow channels of the first face (55), the cross-sectional area at each of these restrictions; flow being less than the cross section of the flow channel access ports of the first group, the first face (55) having alternating flow channels of the first group (553) and flow channels of the second group (554).

The flow guiding plate (53) according to claim 1, wherein each of said flow restrictions (555, 556) extends at least up to three quarters of the depth of the flow channels (563). from the second side.

The flow guiding plate (53) according to claim 1 or 2, wherein each of said flow restrictions (555, 556) includes a wall extending to the bottom of the flow channels (563) of the second face (56).

4. flow guiding plate (53) according to any one of the preceding claims, wherein the flow channels of the first group and the second face have the same cross section in their middle part.

The flow guiding plate (53) according to any one of the preceding claims, wherein the flow channels of the first group and the second group have the same depth over at least three quarters of their length.

The flow guiding plate (53) according to any one of the preceding claims, wherein each flow channel of the second group includes a flow restriction defining a passage between two flow channels of the second face.

7. Flow guiding plate (53) according to any one of the preceding claims, wherein the shape of one face of the sheet is complementary to the shape of the other face of the sheet.

The flow guiding plate (53) according to any one of the preceding claims, wherein said sheet is a sheet of alloy steel, titanium alloy, aluminum alloy, alloy nickel or tantalum alloy.

The flow guiding plate (53) according to any one of the preceding claims, wherein the sheet comprises:

a first flat portion (535) extending between the access ports of the first end of the flow channels of the second face and the flow channels of the first group;

a second flat portion (536) extending between the access orifices of the second end of the flow channels of the second face and the flow channels of the first group.

The flow guiding plate (53) according to claim 9, wherein the first flat portion (535) has first and second through openings (40, 43), and wherein the second flat portion (536) comprises third and fourth through openings (41, 42).

1 1. A flow guiding plate (53) according to claim 9 or 10, wherein said flow channels of the first and second faces have the same depth relative to the first and second flat portions (535, 536).

Flow control plate (53) according to any one of the preceding claims, wherein said sheet has an axis of symmetry.

A fuel cell (1) comprising: first, second and third guiding plates (531, 532, 533) according to any one of the preceding claims;

first, second and third membrane / electrode assemblies (1 1, 12, 13) each comprising a proton exchange membrane and a cathode and anode fixed on either side of the proton exchange membrane;

first and second gas diffusion layers (21);

the first guide plate forming a bipolar plate interposed between the first and second membrane / electrode assemblies (1 1, 12), the first gas diffusion layer (21) covering the flow channels of the first face of the first plate; guide (531) and being in contact with this first face and with the anode of the second membrane / electrode assembly (12);

the second and third guide plates (532, 533) delimiting between them a flow circuit (57) and forming a bipolar plate interposed between the second and third membrane / electrode assemblies (12, 13), the first face of the second guide plate (532) being in contact with the second face of the third guide plate (533), the second gaseous diffusion layer (21) covering the flow channels of the first face and being in contact therewith face of the third guide plate (533) and with the anode of the third membrane / electrode assembly (13).

The fuel cell of claim 13, wherein said first to third guide plates (531, 532, 533) are guide plates according to claim 3, wherein the flow restrictions (555, 556) of the first guide plate (531) are in contact with the first gas diffusion layer (21) and wherein the flow restrictions of the third guide plate (533) are in contact with the second gas diffusion layer (21) .

The fuel cell according to claim 13 or 14, wherein said first to third guide plates (531, 532, 533) are traversed by apertures communicating with said flow circuit (57).

Fuel cell according to any one of claims 13 to 15, wherein said first to third guide plates (531, 532, 533) have identical geometries.